The prior art has provided a steel wire with various metallic coatings in order to add functionalities to the steel wire or in order to enhance its properties. Known metallic coatings on a steel wire are brass for adhesion with rubber, zinc or a zinc-aluminum alloy for corrosion resistance, nickel for a heat resistance.
Zinc coatings are often applied to the steel wire by means of a hot dip process for reasons of economy. Having regard to the time the steel wire is in the zinc bath and to the temperature of the zinc bath, a Fe—Zn interlayer is formed between the steel core and the zinc coating. This interlayer is brittle. Fe—Zn interlayer particles may be spread throughout the zinc coating during further drawing. Due to cracking of the Fe—Zn, sharp crevices are created which are subsequently filled with zinc. This surface damage makes the roughness of the steel wire greater and corrosion of the Fe—Zn interlayer particles at the wire surface leads very fast to red dust spots. Zinc aluminum coatings may have the drawback that the Fe—Al inter-metallic coating grows too fast and is too brittle. The consequence may be the presence of broken particles in the zinc aluminum coating and a fragmentation of the Fe—Al inter-metallic coating.
A nickel coating as such may offer various advantages such as heat resistance, but has the drawback that it deforms not easily and that it may be damaged easily. Hence its processing is difficult and not economical.